Valve installed
I just took my 2016 Seneca in for an oil change and to have the valve installed going into the air tank. Ran into a tech with an attitude who told me putting the valve on would void the warranty. That Freightliner has know about this since the 90s. Unfortunately, I had it checked in 2016 and two very nice and experienced techs could not figure out what made the noise. After moving on to someone more reasonable; the valve was installed and makes a tremendous difference. The pinging is heard occasionally, but much quieter and less often. The part, valve, cost somewhere in the $20 range. Labor was $160.It was covered by warranty. So much more peaceful and less embarrasing.
This site and all the input made all the difference in identifying and getting the problem handled under warranty.
Thank you all!